Wayne Rooney netted his 100th Premier League goal as Manchester United cruised to a 3-0 victory over shell-shocked Arsenal at The Emirates.Sir Alex Ferguson saw Chelsea pull four points clear at the top of the table with their win at Burnley on Saturday night - but the defending champions reduced the gap back to one point with a crushing win over Arsene Wenger's stunned Gunners in the capital.Andrey Arshavin curled two shots wide of the upright while Alex Song hacked the ball off the goalline in the early exchanges of Sunday's 4pm kick-off.But it was the visitors who drew first blood on 33 minutes, when Nani left two defenders bewildered on the right flank with a stunning piece of skill, then jinked to the touchline and dinked the ball over Manuel Almunia, who clawed the ball into his own net with Ji-Sung Park waiting to tuck home at the far post.It was 2-0 four minutes later following a superb counter-attack which was started and finished by in-form England striker Rooney.The 24-year-old picked up possession on the edge of United's 18-yard box, then released Nani who charged towards the Arsenal penalty area, with Park and Rooney in tow. The Portugese winger fed a delicious forward pass into Rooney's path and he slotted a first-time strike into the bottom corner to spark wild celebrations among the men in black.Arshavin dragged a low drive narrowly wide as the hosts tried desperately to claw one back before the break, while Song was also wasteful and off target when he steered a left-footed shot wide on 45.After the break, Almunia was the first keeper to be tested as he scrambled to save Rooney's audacious 20-yard effort, while Cesc Fabregas' 20-yard drive deflected over the crossbar before the Spaniard drew a low diving save from Edwin van der Sar.United slowly started to boss proceedings, though, and made the points safe on 52 minutes when Park latched onto a fine ball over the top from Michael Carrick and benefited from Gael Clichy's hesitant defending to power into the box and slip a sidefooted shot past Almunia with clinical ease.The second half was meandering to an inevitable conclusion until the 80th minute, when Thomas Vermaelen's left-footed strike deflected off Wes Brown to wrongfoot van der Sar and make it 3-1.The goal awoke the home fans from their slumbers and they roared their men on in the closing stages - but United held firm, with Rooney dragging a stoppage-time effort inches wide of the upright, to pull four points clear of Arsenal and remind Chelsea they will fight them tooth and nail for title glory.